Have you ever noticed that pushing a door near its handle is easier than pushing it near the hinges? Or how a seesaw balances perfectly when kids of equal weight sit at the right distance? These everyday examples show the turning effects of force, which is exactly what this chapter is all about!
In this chapter, we learn how forces don’t just push or pull in a straight line, but can also make objects rotate or turn. Understanding this is not only important for exams, but also helps you see physics in everyday life, like using a wrench, balancing objects, or designing simple machines.
🔹 Key Topics You Will Learn:
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Like and Unlike Parallel Forces – How parallel forces work together to move or rotate an object.
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Addition of Forces – How to combine multiple forces to find the resultant force.
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Turning Effect of Force – Understanding moment of force (torque) and how a force causes rotation.
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Resolution of Vectors – Breaking a force into components to make calculations easier.
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Principle of Moments – How bodies balance when forces act in opposite directions.
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Centre of Gravity and Centre of Mass – The point where a body balances perfectly and why it matters.
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Equilibrium – Conditions that keep a body stable, both stationary and rotationally balanced.
Class 9 Physics Chapter 4 MCQs
1. Moment of force is called:
(a) Moment arm
(b) Couple arm
(c) Couple
(d) Torque ✅
2. A body will be in complete equilibrium when:
(a) ΣF = 0 and Στ = 0 ✅
(b) ΣF = 0 and Στ ≠ 0
(c) ΣF ≠ 0 and Στ = 0
(d) ΣF ≠ 0 and Στ ≠ 0
3. In unstable equilibrium, the centre of gravity of the body lies:
(a) At the highest position ✅
(b) At the lowest position
(c) At any position
(d) Outside the body
4. What are like parallel forces?
(a) Forces in opposite directions
(b) Forces of unequal magnitudes
(c) Forces acting along same line
(d) Forces in the same direction ✅
5. The formula to find the magnitude of a vector from its components is:
(a) F = Fx + Fy
(b) F = Fx – Fy
(c) F = √(Fx² + Fy²) ✅
(d) F = Fx × Fy
6. The first condition of equilibrium is:
(a) Net torque is zero
(b) ΣF = 0 ✅
(c) Net acceleration is high
(d) Object is rotating
Class 9 Physics Chapter 4 Short Questions – Turning Effects of Force
Q1: What are like parallel forces?
Ans: Forces that act in the same direction and are parallel to each other.
Q2: What are unlike parallel forces?
Ans: Forces that are parallel but act in opposite directions
Q3: Give an example of a body which is moving yet in equilibrium.
Ans: A boat moving at constant speed in a straight line is an example.
Explanation:
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The body is moving, but it is in equilibrium because the net force acting on it is zero (ΣF = 0).
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Since there is no net acceleration, it continues to move uniformly in a straight line.
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This is also called dynamic equilibrium.
Other Examples:
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A train moving at constant speed on a straight track
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A car moving at constant velocity on a straight road
Q4: Define centre of gravity. How does it affect the balance of a body?
Answer:
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The centre of gravity is the point where the entire weight of a body appears to act.
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If a body is supported at its centre of gravity, it remains balanced and does not rotate.
Q5: What is the difference between centre of gravity and centre of mass? Give one example.
Answer:
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Centre of Gravity (CG): The point where the total weight of the body acts.
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Centre of Mass (CM): The point where the entire mass of the body is considered to be concentrated
🔹 Why This Chapter is Important:
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Helps you understand real-life examples like levers, pulleys, doors, seesaws, and machines.
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Builds a strong foundation for mechanics, engineering, and rotational motion.
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Prepares you for exam questions, including numerical problems, long answers, and conceptual questions.
📥 Download Class 9 Physics Notes 2026 – Turning Effects of Force (Punjab Board)
Skip to PDF contentGet complete notes for Chapter 4, including:
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Easy-to-understand explanations
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Important formulas and examples
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Exam-focused questions
📥 Click to Download Chapter 4 Notes – Turning Effects of Force